1. Field of the Invention
The present invention relates to a method for data reproducing from a compact disk (CD-ROM) drive, particularly to a method for data reproducing from a CD-ROM drive wherein the range of Cache Hit addresses is the maximum size of the buffer memory so that the data reproducing efficiency is enhanced by a high Cache Hit ratio.
2. Description of the Prior Art
The continuous progress of technology has produced various kinds of optical storage devices, such as CD-ROM, CD-R, CD-RW and DVD-ROM drives etc. Most of them rotate at a maximum speed more than 20×. The maximum reproducing speed of CD-ROM drive at 1× is 150 Kbps which is the normal speed for music CD (CD-DA) playback. That is to say, most of the optical storage devices have a maximum reproducing speed more than 20× (20×150 Kbps=3 Mbps).
However, the above-mentioned reproducing speed is used when the data is read by sequential access method. Random data access is likely to be carried out at a speed less than {fraction (1/10)} of the maximum reproducing speed of optical disk drives. Disk drives spend much time in tracking, reading and decoding. Therefore, a buffer memory is used to temporarily store data already accessed or pre-stored part of data from the disk so that the data reproducing is improved by Cache Hit.
The Cache Hit ratio is proportional to the size of the buffer memory. Data is transmitted directly from the buffer memory to a host, and tracking, reading and decoding are skipped when the data already exists in the buffer memory.
In conventional optical storage devices, when the data stored in the buffer memory is transferred to the host, it is regarded as Cache Miss. That is to say, Cache Hit indicates that data are decoded and waiting to be transferred to the host. As shown in FIG. 1, a buffer memory 11 has a maximum size of N (e.g. megabyte). The data read from the disk is stored in an address R 111, the decoded data is stored in an address D 112 and the transferred data is stored in an address T 113. The boundary of the buffer memory is B 114. The data stored between the boundary B114 and T 113 is regarded as Cache Miss. Only the data stored in the address between D 112 and T 113 is considered as Cache Hit. The Cache Hit addresses are located between T and T+X1. Thus, even though the data is stored between the boundary B 114 and T 113 and remain in the buffer memory, the data is regarded as Cache Miss.
The above-mentioned method for Cache Hit is suitable for data reproducing by sequential access but not random access. Therefore, the optical storage devices adapted to UDF (Universal Disc Format) and using random access, such as CD-R/RW drives, will have a low Cache Hit ratio and the data reproducing speed will be fairly low with the conventional method.